VSE riaa equalizer phono stage

Hesky · 2004-10-26 10:26 pm

Hi all,

Has anyone had any experience with the Vacuum State Electronics FVP5A phono stage? The input impedance of my pre-amp is 50k so I though the riaa stage would be pretty compatible (leave out the line stage).
My initial idea was to use a smooth non regulated B+ supply as the current draw would be pretty low. Is this "SuperReg" a specific design or just a 250v regulated supply?

Cheers
Hesky

fdegrove · 2004-10-27 1:07 am

Hi,

The input impedance of my pre-amp is 50k so I though the riaa stage would be pretty compatible (leave out the line stage).

That should work fine but read the note on the schematic warning against some attenuators.

Is this "SuperReg" a specific design or just a 250v regulated supply?

It is not specific to the phonopreamp you want to build but is fully explained in AWs Tube Preamp Cookbook.

Cheers,

Hesky · 2004-10-27 1:58 am

Hi frank,

That should work fine but read the note on the schematic warning against some attenuators.

I noticed that, my home made pre-amp uses an alps blue pot so it shouldn’t be a problem.

I think I should "take my stabilizes off" so to speak and design my own regulated b+ supply for this phono stage.

I'd like to design my own phono stage, but I'm not confident (smart is a more appropriate word) enough to tackle the calculations required to select values for an riaa circuit, not yet anyway.

Thanks
Hesky

pedroskova · 2004-10-27 3:20 am

This circuit is a cascode input in which the fet replaces the traditional bottom triode. If you want to stay "all tube", you might look at this Steve Bench design. I haven't heard Mr. Wright's design, but Mr. Bench's definately rocked my boat.

It also needs a regulated(quiet) psu.

You can't go wrong either way.

Hesky · 2004-10-27 7:10 pm

Hi Pedro,

Thanks for the link to Steve's phono design, I navigated my way around to his site and its a real interesting read!! He's attempted five phono designs and really rates the one you linked.
I'm very tempted.

It sounds like you have already built one of his phono designs.

Thanks

pedroskova · 2004-10-27 7:17 pm

Hesky said:
It sounds like you have already built one of his phono designs.

Thanks

Yep, that's the one that I built. It's easily the best phono stage that I've ever owned.

As far as Mr. Wright's stage, I think Brett, who posts on this forum, has built it - and really likes it.

Hesky · 2004-10-27 7:39 pm

Hi Pedro,
What sort of B+ supply did you use? regulated or a real smooth non regulated suppy.
He says the circuit can run from anything from 170 volts to 250 volts. 250 volts gives a bit more gain and a little less distortion. The downside is it consumes more current, which isnt much of a problem.

Cheers

pedroskova · 2004-10-27 7:54 pm

Hesky said:
Hi Pedro,
What sort of B+ supply did you use? regulated or a real smooth non regulated suppy.
He says the circuit can run from anything from 170 volts to 250 volts. 250 volts gives a bit more gain and a little less distortion. The downside is it consumes more current, which isnt much of a problem.

Cheers

I'm using 2 OC3's per channel for the phono stage. The output to the line stage has since dropped to ~250V since I changed over to 12B4A's.

here's the schematic:

An externally hosted image should be here but it was not working when we last tested it.

djmiddelkoop · 2004-10-27 10:17 pm

Hesky,

I 've build the FVP5A and it's definite the best and most quiet MCphono stage I ever build.

The superreg is a special powersupply that I really recommend.
It makes the FVP really sing.

Dick.

Hesky · 2004-10-28 12:56 am

The superreg is a special powersupply that I really recommend.

Hi dick, I was thinking about building my own regulated B+ supply based on the mje340 transistor and the 317t voltage regulator. maybe tube rectified.

Pedro, your B+ supply looks pretty sweet, cant help but think how hard it would be to get hold of those OC3 voltage regulator tubes!

Just a few questions, is it beneficial to also us an isolation transformer? and how exactly does the 10m45s current regulator and the OC3 voltage regulator work together, what are they doing moreover?

Cheers

pedroskova · 2004-10-28 1:49 am

Hesky said:
Pedro, your B+ supply looks pretty sweet, cant help but think how hard it would be to get hold of those OC3 voltage regulator tubes!

Thanks...$4.95 each...plenty out there

Just a few questions, is it beneficial to also us an isolation transformer? and how exactly does the 10m45s current regulator and the OC3 voltage regulator work together, what are they doing moreover?

Cheers

I put the isolation transformer in there because I originally intended to add an outlet for my turntable. This would place t.t. and preamp at the same ground potential. Haven't tried it yet, but I added it anyways because I got it off of ebay for 20 cents on the dollar.

The OC3 tubes act as shunt voltage reulators. With VR tubes, you need to make sure that they get their minimum working current, while ensuring that they don't exceed their maximum allowable working current(in addition to your circuit's current needs). Traditionally, you could just put a resistor before them that meets the requirements, but the cheap IXYS ccs simplified everything while adding the benefits of a ccs.

Also, the capacitor bypassing the vr tubes exceeds manufacturer's recommendations, and shouldn't be used without the accompanying resistor. I can hunt down the thread from the diy tube asylum that explains this if you're interested.

regards

fdegrove · 2004-10-28 2:11 am

Hi,

I can hunt down the thread from the diy tube asylum that explains this if you're interested.

If it's not too much trouble, I'd certainly be interested.

TIA.

Cheers,

Hesky · 2004-10-28 2:17 am

ah I get it, so these ixys ccs chips are there mainly to protect the oc3 voltage regs. pretty cunning!

These little current regs could prove pretty useful, just going off topic a little but I was thinkin about the possibility of using them in a tube rectified power supply to limit the inrush current into any smoothing caps, meaning that larger caps could be used

cheers

fdegrove · 2004-10-28 2:31 am

Hi,

ah I get it, so these ixys ccs chips are there mainly to protect the oc3 voltage regs.

Actually, not quite: they sort of replace the voltage dropping and hence current setting resistor for the VR tubes.
These need to be set roughly in the middle of their current operating range to be precise (voltagewise).
These VRs also require some ignition voltage for the gas to ionise. After which they'll clamp the HT rail according to the voltage spec of the type of VR tube, the CCS will allow for this as well.

So essentially, as far as the circuit behind this arrangement is concerned, you combine the benefits of a constant current source together with the superiority of a shunt voltage regulator.

just going off topic a little but I was thinkin about the possibility of using them in a tube rectified power supply to limit the inrush current into any smoothing caps, meaning that larger caps could be used

Use a choke and you're done with it...

Cheers,

pedroskova · 2004-10-28 2:55 am

fdegrove said:
Hi,

If it's not too much trouble, I'd certainly be interested.

TIA.

Cheers,

Hi,

This is one thread that discusses the theory behind this. "Voltsecond" provides an understandable (even for me) explanation. I was just too chicken to follow his ideas beyond what Mark Kelly had already shown to work.

Series inductance of Glow Diodes.

If you search the tube diy asylum using "kelly glow diode", you can find some more discussions.

regards

fdegrove · 2004-10-28 3:09 am

Hi,

If you search the tube diy asylum using "kelly glow diode", you can find some more discussions.

Thank you for digging it up.

The reason I ask is that I'm badly documented on some of the more "unconventional" applications of VR tubes especially when used as shunt regs.

Cheers,

Brett · 2004-10-28 8:50 am

pedroskova said:
Yep, that's the one that I built. It's easily the best phono stage that I've ever owned.

Actually, second best. The RTP3C is better, but I use(d) both.

As far as Mr. Wright's stage, I think Brett, who posts on this forum, has built it - and really likes it.

I've built both, and in it's last incarnation before I moved house for work, the preamp had one of each in use; the RTP3C for the MC and the FVP for the Decca as it's single ended due to it's sum/diff generator. Powersupply was similar to pedroskova's in post#8, but I used a Superreg for the cascode stages, in the final version with a Pimm BBMCCS instead of the VS LM317 based version after the inital CLC. The 12B4A's were fed from a simple C (small) LCLC supply. I'd have liked to have messed further with a CCS - VR diode supply, but I moved for work and it all went into storage 'till I get home again. Rectifiers were 6CJ3 in FW.

I didn't use the SLCF stage as I prefer my 12B4A (Diff and SE) and had an S&B TX102 volume control after the 12B4A as well as all my line switching. The bottom tubes in the cascodes and the 12B4A's had their heaters raised about 40V and were fed from 317 based CCS. The top tubes were sat at about +140V on the heaters and again CCS fed.

So my pre is a long way from Allen's original spec (and the PS is HUGE). The hybrid cascode front end is a killer, especially with MAT02's) and the SLCF is great too, but I really like the S&B volume controls, and the simpler 12B4 stage sounded marginally better into them in my system.

VSE riaa equalizer phono stage

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